1. Field of the Invention
This invention relates to a crosslinkable polymer composition, the preparation thereof and the use thereof.
2. Background Art
Textile sheet materials produced by the customary methods for producing nonwovens, for example by the airlay, wetlay or spunlay process, require a binder for durable binding of the fibers and for increasing the resistance to mechanical stress. Even today mechanically consolidated textile sheet materials such as wovens, nonwoven scrims or needled fleece mats require a binder for certain applications. These applications include for example the consolidation of pulled cotton fiber mats produced by means of an aerodynamic process, the consolidation of needled natural fiber mats, binders for preforming high performance fabrics in composite applications, the lamination of high strength fabrics in ballistic applications, prebinding of fleece mats for fiber-reinforced thermosets or the binding of pulverulent substances into a textile sheet material such as activated carbon into filters or flame-retardant graphite on roof membranes.
These binders are customarily based on synthetic macromolecular compounds and, in the prior art, can be applied either in the form of solids, for example as powder, granulate or fiber, or in the form of liquids, for example as aqueous polymer dispersions or solutions. The increased strength of the textile sheet materials is due to the bonding of the fibers by the polymers which adhere to the fiber and so strengthen the fibrous structure.
WO-A 90/14457 discloses a process wherein carded glass fibers are mixed with thermoplastic powder, for example polypropylene, polyester or polyamide, and the fibrous structure is subsequently consolidated at elevated temperature and pressure. AU-B 36659/89 likewise describes a process for consolidating glass fiber materials by means of thermoplastic powders. The use of polyesters or polystyrene is recommended. The low strength of the thus bonded fibrous structures on contact with water or solvents is disadvantageous.
Since the glass transition temperatures or the melting temperatures of the binders are frequently exceeded at elevated temperatures, durable chemical crosslinking of the binders is required in order that a high temperature dimensional stability may be conferred on the fibrous structures. Processes are known for consolidating fiber materials composed of polyester, polyamide or cotton fibers using self-crosslinking polymer dispersions EP-A 80144 (U.S. Pat. No. 4,451,315). True, nonwoven fabrics of high strength are obtained, but the use of aqueous binders is prohibitively costly on the drying side. In addition, it is not a straightforward matter to disburse the binder in the fiber matrix.
U.S. Pat. No. 4,612,224 describes the consolidation of pulverulent crosslinkable copolymers based on phenol-formaldehyde resins. The disadvantage with this binder system is the large amount of formaldehyde emitted in the course of the production and use of the fiber materials thus consolidated.
WO-A 94/20661 (U.S. Pat. No. 5,668,216) describes self-crosslinking redispersible dispersion powders based on N-methylolacrylamide-containing vinyl ester copolymers or (meth)acrylic ester copolymers as fiber bonding agents. The disadvantage with this binder system is its relatively high melt viscosity in that setting requires an appreciable input of water into the fiber matrix.
DE-A 2701490 (U.S. Pat. No. 4,129,545) describes thermosetting copolymers based on acrylic esters and/or vinyl esters and additionally containing (meth)acrylic esters of mono- or polyfunctional hydroxycarboxylic acids and N-alkoxyalkyl(meth)acrylamide as crosslinking component for use as a powder paint.
EP-A 721004 discloses crosslinkable water-dispersible powders is including both filming polymers having at least one functional group and reactive components which form chemical bonds on dispersion of the powders in water. Aqueous dispersions of this polymer blend are useful for coating applications. There is no mention in this patent application of utility for fiber bonding in nonwovens.
EP 894888 (U.S. Pat. No. 5,977,244) discloses chemically crosslinkable polymer powders comprising a dry pulverulent thermoplastic copolymer preparation based on the one hand on aqueous copolymer dispersions having a glass transition temperature above room temperature and on the other on a solid reactive crosslinker component having a melting point of less than 150° C. The disadvantage with this binder composition is that the chemical crosslinker agents sed therein do not have universal agility, but have to be compatible with the polymers to be crosslinked. Furthermore, in these self-crosslinking systems, a chemical crosslinking reaction can take place only after appropriate diffusion of the crosslinker substances into the polymer matrix.
U.S. Pat. No. 5,869,568 has room temperature crosslinking aqueous polymer dispersions consisting of two-phase polymer particles having a core of epoxy-functional copolymer and a shell of carboxyl-functional copolymer and low molecular weight epoxy-functional epoxy compounds enclosed between the phases. These systems are based on a core-shell structure that requires a relatively complicated polymerization process to actualize.
It is an object of the present invention to provide binders, especially for consolidating and for laminating fiber materials, that may be used in powder form, that process with a lower melt viscosity than the prior art and substantially without emitting harmful substances, and that confer high strength and heat resistance on the fibrous structure after processing.